This invention relates to knives. In particular, this invention relates to a retractable utility knife with improved blade support and blade replacement features.
Utility knives are used in a variety of commercial and domestic applications, including construction, household repairs, arts and crafts and many others. Utility knives provide the advantage of being extremely sharp, and are typically loaded with a blade which is scored into segments, so that as the tip of the blade becomes dull the end segment can be broken off and the user can continue using the knife by exposing the next successive segment, which is still sharp.
However, utility knives present a number of disadvantages, particularly in heavy duty applications such as construction. Eventually, when the last segment has been broken off of the blade, the blade must be replaced. Conventionally, this requires removing the sliding body which retains the blade in the knife handle, attaching a new blade, and replacing the sliding body into the knife handle. This can be a difficult operation to perform without a surface to rest the knife on (for example while on a ladder), and increases opportunities for injury because of the manipulation required in order to hold the blade on the sliding body while inserting it into the knife handle.
Moreover, in heavy duty applications there is a considerable amount of force experienced by the blade, for example when cutting wallboard and other surfacing materials, which tends to deflect the blade laterally. The primary resistance to deflection of the blade within the handle is provided by the throat of the handle, which conventionally provides a single layer of supporting surface (generally metallic) on each side of the blade. Accordingly, over time the cutting force on the blade tends to widen the throat of the knife handle, which in turn allows the blade to deflect more when in use. This results in inaccurate cuts and the blade segments breaking off prematurely.
It would accordingly be advantageous to provide a utility knife with a quick release feature which allows the blade to be changed without removing the sliding body from the knife handle and with minimal manipulation. It would further be advantageous to provide a knife structure which reinforces the throat of the knife, thereby reducing deflection of the blade during use and thus minimizing opportunities for inaccurate cuts and premature breakage of the blade.
The present invention provides a utility knife having a quick release feature, whereby forcing the sliding body toward the throat of the knife handle releases the blade, so that a new blade can be inserted easily and without removing the sliding body from the knife handle.
The invention accomplishes this by providing a resilient blade engaging member, biased to the locked position, which engages an opening in the blade in normal use. When the blade engaging member is pushed against the end of the guide slot in which the sliding body travels, it automatically releases from the blade allowing the blade to be removed from the knife handle and a new blade positioned and engaged therein.
The present invention further provides a knife handle structure which reinforces the throat of the knife, to better restrain the knife blade against deflection and thus to prolong the life of the knife blade and facilitate the accuracy of cutting with the knife.
The invention accomplishes this by providing a knife handle having a double channel configuration, comprising an outer channel providing a blade retaining surface and an inner channel inverted relative to the outer channel and providing a supporting surface for the blade. In the preferred embodiment the outer channel is tapered toward the inner channel about the throat of the knife, to reinforce the throat and prevent deformation under the stresses imparted by the knife blade when in use.
The present invention thus provides a knife, comprising a handle, comprising an outer channel having a back surface, side surfaces and retaining flanges depending inwardly from the side surfaces, an inner channel comprising blade supporting surface and sides, the sides abutting the side surfaces of the outer channel and the blade supporting surface being spaced from the retaining flanges for slidably receiving a blade therebetween, and a sliding body for engaging the blade trapped between the retaining flanges and the blade supporting surface, the sliding body having a locking member for locking a position of the sliding body within the handle.
In further aspects of the invention, the inner channel is disposed in inverted relation to the outer channel; a portion of the back surface of the outer channel tapers toward the blade supporting surface and abuts the blade supporting surface at a throat of the knife; the locking member comprises a locking bolt extending through the sliding body and through a guide slot in the blade supporting surface and into a nut trapped between the sides of the inner channel; the blade engaging member comprises a blade engaging member for engaging the blade to the sliding body, the blade engaging member comprising a body portion and a resilient blade engaging arm projecting from the body portion, the blade engaging arm having a blade engaging projection for extending through an opening in the blade, and a cam finger extending through the guide slot disposed between the blade engaging projection and an end of the guide slot adjacent to a throat of the knife, whereby when the sliding body is moved so that the blade engaging finger is pressed against the end of the guide slot the blade engaging projection recedes from the opening in the blade to disengage the blade from the sliding body; the back surface of the outer channel comprises an opening through which the cam finger extends when the blade engaging projection recedes from the opening in the blade; and/or a pocket clip is affixed to an opening in the blade supporting surface and covers an end of the handle opposite the throat of the knife.
The present invention in a further embodiment provides a knife, comprising a handle, comprising an outer channel having a back surface, side surfaces and retaining flanges depending inwardly from the side surfaces, a blade supporting surface having a guide slot, spaced from the retaining flanges for slidably receiving a blade therebetween, and a sliding body trapped between the retaining flanges and the blade supporting surface, the sliding body having a locking member disposed through the guide slot for locking a position of the sliding body within the handle, and comprising a blade engaging member for engaging the blade to the sliding body, the blade engaging member comprising a body portion, and a resilient blade engaging arm projecting from the body portion, the blade engaging arm having a blade engaging projection for extending through an opening in the blade, and a cam finger extending through. The guide slot, disposed between the blade engaging projection and an end of the guide slot adjacent to a throat of the knife, whereby when the sliding body is moved so that the blade engaging finger is pressed against the end of the guide slot, the blade engaging projection recedes from the opening in the blade to disengage the blade from the sliding body.
In further aspects of the further embodiment of the invention, a portion of the back surface of the outer channel tapers toward the blade supporting surface and abuts the blade supporting surface at a throat of the knife; the back surface of the outer channel comprises an opening through which the cam finger extends when the blade engaging projection recedes from the opening in the blade; the blade supporting surface is part of an inner channel is disposed in the outer channel; the inner channel is disposed in inverted relation to the outer channel; the locking member comprises a locking bolt extending through the sliding body and through a guide slot in the blade supporting surface and into a nut trapped between the sides of the inner channel; and/or a pocket clip is affixed to an opening in the blade supporting surface and covers an end of the handle opposite the throat of the knife.